With the advancement of industrial society into the high information age, the importance of electronic display devices as a medium for displaying and transferring various pieces of information is increasing. In particular, a liquid crystal display (LCD) is a technology-intensive device that incorporates liquid-crystal and semiconductor techniques, and is advantageous because it is thin and lightweight and consumes little power, and thus research and development into structures and fabrication methods thereof is ongoing, and it is useful in diverse fields.
Such an LCD device includes an additional light source on the rear side thereof to thus exhibit a color and an image because liquid crystals themselves cannot emit light.
An example of a light-emitting device includes a backlight unit (BLU). As an LCD device is recently manufactured to be slim, the use of LEDs (Light-Emitting Diodes) in place of conventional CCFLs (Cold Cathode Fluorescent Lamps) is rapidly increasing. LEDs (Light-Emitting Diodes) do not use mercury and manifest excellent color reproducibility.
Compared to a direct-type LED in which the LED is distributed on the front side of the backlight unit, an edge-type BLU in which the LED is distributed on the lateral sides thereof is advantageous in terms of power consumption and product thickness, and application thereof is thus increasing.
An edge-type BLU includes a light guide plate able to emit a light source to the front side from the lateral side. Light generated from the light source is incident from the lateral side of a light guide plate to the inside of the light guide plate and is then emitted to the front side thereof. In this way, the path of light passing through the light guide plate is relatively long, thus increasing light loss. In order to prevent this phenomenon, a polymethyl methacrylate (PMMA)-based material having high transmittance is mostly used. However, the PMMA-based material is weakly resistant to water due to its chemical structure and thus a light guide plate using the same suffers from warpage and poor dimensional stability under high-temperature and high-humidity conditions.
In this regard, Korean Patent Application Publication No. 10-2012-0088944 (Laid-open date: Aug. 9, 2012) discloses a light guide plate having multiple layers, comprising a pattern layer having a pattern and formed of a material having high MMA content, and a cover layer formed of a material having low MMA content, which are laminated together. It has been described that such a light guide plate may overcome yellowing problems due to laser or thermal processing.